The invention relates to an inductive starting sensor for battery powered coin acceptors.
Battery powered, electronic coin acceptors should be designed in such a manner that they exhibit a low current requirement both during the operating phase as well as during the rest phase. It is therefore known from German Application No. G 86 24 368 that such coin acceptors can be designed so that they are not "wakened" until when requested. In the rest state the structural parts and components of the electronic coin acceptor are inactive. In this manner the current requirement can be minimized during the rest phase.
The waking of such an electronic coin acceptor takes place with the aid of a starting sensor which is likewise known from German Application No. G 86 24 368 and which can operate inductively. It determines when a coin has been inserted into the coin acceptor. This brings about a damping from which a starting signal can be derived. It is essential for such starting sensors that they are able to operate in a broad temperature range from -30.degree. to +80.degree. C. It would be conceivable to use a temperature compensated integrated circuit for this circuit. However, an integrated circuit can not be used for reasons of current consumption. The current requirement should be less than 10 .mu.A.
Other prior art transistor circuits can also be used. However, relatively large tolerances over the required temperature range result from the use of field effect transistors or bipolar transistors in appropriate electronic circuits so that a reliable response of the starting sensor is not always assured. There is also the danger in the case of the known circuits that if the oscillator fails, e.g. in the case of extreme dewing, a continuous waking signal is produced which naturally puts a load on the battery.